The present invention relates to hole formation in turbine components and more specifically to the formation of complexly shaped film holes and a method for making same by additive manufacturing.
Airfoils in a turbine engine often include cooling holes for discharging a film of cooling air along the outer surface of the airfoil to affect film cooling. These may be referred to as “film cooling holes” or “film holes.”
In order to improve the performance of cooling holes it is also known to modify their shape to affect cooling flow diffusion. The diffusion reduces the discharge velocity and increases the static pressure of the airflow. Diffusion cooling holes are known in various configurations for improving film cooling effectiveness by providing a greater coverage of coolant film on the hot surfaces of components. A typical diffusion film cooling hole may be generally conical from inlet to outlet with a suitable increasing area ratio for affecting diffusion without undesirable flow separation. Typical diffusion film cooling holes also incorporate a metering section at or near the inlet to control the flow rate to a desirable magnitude. Diffusion occurs along at least a portion of the length of the hole, typically towards the exit, and may be in the lateral and/or longitudinal directions, or combinations thereof. Other types of diffusion cooling holes are also found in the prior art including various generally rectangular-shaped hole exits to provide varying performance characteristics.
Conventional methods for forming film holes include casting and machining. One problem with film holes produced by conventional methods is they are limited in shape by the manufacturing process.
Therefore there is a need for a manufacturing process for producing complexly shaped film holes in turbine blade components. Such complex film holes allow for precise delivery of cooling fluid such that the cost of such cooling fluid in lost engine efficiency is minimized and/or reduced.